Isothiazole derivatives are widely known as intermediates to be used for pharmaceuticals and a agricultural chemicals, intermediates for functional coloring matters, and electronic materials. Various studies have heretofore been made processes for producing isothiazole derivatives (please refer to Non-Patent Document 1 and Non-Patent Document 2). Among these production processes, 3,4-dichloro-5-cyanoisothiazole, which is can easily be subjected to a functional group conversion thereof, has been used as an intermediate for pharmaceutical compounds and agricultural chemicals. In fact, this compound has been used as an important intermediate for a agricultural chemical, as disclosed in JP-A (Japanese Unexamined Patent Publication; KOKAI) No. 5-59024, and Japanese Patent No. 4,088,036. However, the production process disclosed in the above-mentioned Non-Patent Document 1 can only provide a low yield of the product. Further, the production process disclosed in the above-mentioned Non-Patent Document 2 cannot produce 3,4-dichloro-5-cyanoisothiazole having a specific structure, which is useful as an important intermediate for an agricultural chemical.
A process using carbon disulfide (CS2), sodium cyanide (NaCN) and chlorine (Cl2) has heretofore been known as a process for producing 3,4-dichloro-5-cyanoisothiazole (please refer to Patent Document 1). However, this process has such drawback that a specially flammable material such as CS2 is used as a raw material to be used therein, and also has another drawback that a toxic material such as NaCN is used therein. In addition, this process exhibits a low yield and is an ineffective process, and also has a drawback that a large amount of wastes are produced as by-products. Examples of the wastes may include by-produced sulfur. In this process, chlorine is introduced into a reactor containing therein dimethylformamide (DMF) as a solvent under heating, and therefore, runaway of a reaction can occur. Further, a 3,4-dichloro-5-cyanoisothiazole derivative which has been produced by this process contains a large amount of tar components, the product must be purified in a purification step such as distillation, and accordingly this process is not an industrially preferred production process. As another production process, a process using trichloroacetonitrile and sulfur is known (please refer to Patent Document 2). However, this process is not an industrially preferred production process, because it exhibits a low yield and is ineffective, and also requires a high reaction temperature. Further, a process using dichlorofumaronitrile and sulfur is also known (please refer to Patent Document 3). However, this process is not an industrially preferred production process, because it only provides a low yield and is ineffective, and also because a high reaction temperature is required therein.